This invention relates to a sliding bearing assembly, particularly to a half sliding bearing assembly.
For the purpose of recent compacting and weight-saving or the like, the stiffness of a housing to be fitted with a sliding bearing has been lowered by thinning the wall of the housing, using an aluminum alloy, or the like. Therefore, a slight repetitive strain accompanying dynamic load becomes easier to cause in the housing and the bearing than before. In addition, in the big end bearing of a connecting rod or the main bearing in an internal combustion engine, a high speed, a high temperature and a high load have been required for a high output engine. Between the internal surface of the housing of the above big end portion or main bearing portion and the back of the sliding bearing with which the internal surface of the housing has been fitted, a relative, slight collision and slight sliding are caused accompanying the repetitive strain of the housing and the bearing, whereby a damage due to fretting abrasion has become easy to cause.
As a measure for the above fretting abrasion, there have heretofore been known a sliding bearing in which a coating layer of a resin type excellent in lubricity such as PTFE or the like is provided on the back of the sliding bearing and the sliding bearing in which such measures as providing a coating layer by plating with silver or copper and the like have been taken.
JP-A-61(1986)-88,020 discloses a sliding bearing in which a coating layer is formed of an alloy of copper, nickel, aluminum or the like having a hardness of Hv 15 to 80 on the back of the bearing. It states that these soft metal coating layers inhibit the fretting abrasion from being caused.
JP-A-2(1990)-89,813 discloses a sliding bearing in which the coating layer is a complex plating layer formed by simultaneously depositing PTFE and Ni or Co. This means that a complex plating layer of PTFE and Ni or Co is formed in order to prevent the PTFE from being peeled owing to its inferior bonding strength to the backing metal. It states that the fretting resistance can be well enhanced by preventing PTFE having a low friction coefficient from being peeled as mentioned above.
Moreover, JP-A-6(1994)-94,036 of the present Applicants discloses a sliding bearing in which as the coating layer, a phosphate film has been provided on the backing metal. This intends to enhance the fretting resistance by providing a phosphate film having a low friction coefficient.
However, with the soft coating layer composed of a metal having a hardness of Hv 15 to 80 stated in JP-A-61(1986)-88,020, an adhesion phenomenon tends to appear between the housing and the back of the bearing because of the insufficient stiffness of the coating layer, and fretting accompanying the adhesion phenomenon becomes easy to cause, so that by only softening the coating layer, no sufficient fretting resistance has been obtained.
Moreover, in the coating layer composed of PTFE and a metal such as Ni or the like stated in JP-A-2(1990)-89,813, there is still a case where PTFE is allowed to fall out by a slight abrasion between the housing and the back of the bearing, and it has been impossible to obtain sufficiently good fretting resistance.